PHP - preg_replace : no replace if data attribute is found in image

Question

I'm trying to clean some pages from my blog and modify the images tags by using preg_replace. When an image has been cleaned, I add the data attribute data-updated to avoid modifying them a second time.

$final =  preg_replace('/<img(.*?)>/', '<img$1 data-updated=\'1\'>', $final);

But the next time I run the cleaning, the data-updated attribute is added a second time. I could do a str_replace to remove the additional data-updated but I'd like to avoid adding it through a regex in the first place.

i have tried using [^data-updated] with no success and I have found a similar post here: preg_replace expression can't include string but replacing data-fancy by data-updated doesn't work

Is there a way to only add data-updated if it's not already there? There are many other tags in the so I need to be able to check the presence of data-updated anywhere in the img tag

Here is an example of such an image:

<img srcset="xxx" src="yyy" loading="lazy" data-style="aspect-ratio:4/3;" data-placeholder="4-3" data-updated="y" alt="" width="100%">

Thanks! Laurent

[^data-updated] negates a character class, here specifically not matching adeptu-. You can't use that syntax for negating strings. If you do want to use regex, you'd want to use a negative lookahead instead. — Markus AO
– Markus AO, Commented Apr 4, 2022 at 19:38

Sammitch · Accepted Answer · 2022-04-04 19:01:52Z

2

Nested structures like HTML are notoriously difficult to parse with regular expressions, because those structures are irregular. Not to mention that what you explicitly need is a parser since you need to test for the presence of attributes before making modifications.

For this, there is DOM. Eg:

$html = <<<_E_
<html>
<head>
    <title>Hello world</title>
</head>
<body>
    <div>
        <h1>Hello World!</h1>
        <img src="/images/foo.jpg">
    </div>
    <div>
        <img someattr="yes" src="/images/bar.jpg">
    </div>
</body>
</html>
_E_;

$d = new DomDocument();
$d->loadHtml($html, LIBXML_HTML_NODEFDTD);

foreach($d->getElementsByTagName('img') as $node) {
    if( $node->attributes->getNamedItem('someattr') === null ) {
        $node->setAttribute('someattr', 'alsoyes');
    }
}

echo $d->saveHTML();

Output:

<html>
<head>
    <title>Hello world</title>
</head>
<body>
    <div>
        <h1>Hello World!</h1>
        <img src="/images/foo.jpg" someattr="alsoyes">
    </div>
    <div>
        <img someattr="yes" src="/images/bar.jpg">
    </div>
</body>
</html>

answered Apr 4, 2022 at 19:01

Sammitch

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1 Comment

Laurent Over a year ago

you are right, it's the best approach, I was using a DOM parser to create the clean image, I now use it to mark it as clean and wrap it into a div without using regex. Thanks for pointing out!

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